Over the last decade, specialty lenses have advanced in tremendous ways. New designs, materials, and solutions have given practitioners the opportunity to fit more patients in innovative ways. Scleral lenses have led the charge in these advances. Several noteworthy advancements are making scleral lenses a preferred option when specialty lenses are required. These advancements have also given practitioners the ability to offer these technologies for more corneal conditions.

Design An increased understanding of the way that scleral lenses interact with the ocular surface has promoted unique design advancements. A successful scleral lens fitting includes central corneal clearance of between 50µm to 200µm after lens settling, appropriate limbal clearance, and appropriate scleral landing zone interaction with the conjunctiva and sclera on which the lens rests.¹

Traditional scleral lens designs did not compensate for the curves in the limbal region. As such, more inherent challenges existed to achieve appropriate limbal clearance. Often, this would require practitioners to reach for larger-diameter lenses to adequately clear the limbal region of the cornea. As the lenses become larger, their additional weight made it challenging to keep them vertically centered on the ocular surface. Contemporary scleral lenses are designed with a reverse curve in the proximal portion of the limbal clearance region. This increases the likelihood that limbal clearance will occur, usually with the initial scleral lens designs and without the need for further modification.²

Another noteworthy advancement in lens design is the use of standard toric peripheral curves in the scleral landing zone. Traditional designs were made with a spherical landing zone. Through further research on the shape of the sclera, we realized that some individuals experienced an uneven distribution of the landing zone bearing on the conjunctival tissue.³ As such, the lens landing zone would rest along the conjunctiva or impinge the conjunctiva in certain regions and would be lifted away from other regions of the ocular surface.

Much work has been done with regard to understanding the shape of the eye beyond the cornea where the lens lands. It is now well accepted that most patients have a scleral shape that is not spherical.^4,5 As such, many contemporary scleral lens diagnostic sets have been created with toric peripheral curves. This has helped clinicians determine better starting points with the initial scleral lenses that are selected and being placed on eyes. Acute attention should still be paid to how the landing zone is interacting with the conjunctiva to ensure an appropriate fitting relationship.

Materials Significant advancements in materials have also occurred in the last several years. The first is the advent of a polyethylene glycol (PEG) surface treatment. The properties of this polymer allow it to optimize surface water retention, resulting in a hydrophilic surface. This increases lubricity and optimizes patient comfort.⁶ Interestingly, because of its hydrophilic properties, it resists lipid deposition on the surface of the lens.

There are certain factors to consider to optimize the performance of this coating and to maintain its integrity on the surface of the lens. This really involves selecting the appropriate care solutions to use with the treated lenses. No abrasive cleaners or any cleaners containing alcohol or polishes should be used with GP lenses that are coated with PEG. However, there are several approved multipurpose solutions and hydrogen peroxide systems that are approved to be used with lenses coated with PEG.

Another advancement is the introduction of a hyper-permeable material that has a Dk of 180.9 This is noteworthy, as practitioners have always been cognizant of oxygen demands on the ocular surface; in fact, these oxygen requirements have been the basis of many central corneal clearance guidelines. This new hyper-breathable material provides additional security in practitioner efforts to deliver adequate oxygen for the most compromised corneas.

Solutions There are two main categories of solutions needed for the care and wear of scleral lenses. The first category is those solutions that are needed to clean, disinfect, and store the lenses. The second are those solutions that are required to support the lens on the eye (i.e., the filling solution that is placed in the lens prior to lens placement on the eye).

Traditionally, inhalation saline solution has been utilized to fill the bowl of a scleral lens prior to application. This solution comes as individually packaged 0.9% sodium chloride vials that provide preservative-free solution to the bowl. One commonly used saline does tend to be more acidic compared to commercially available filling solutions for scleral lenses.^7,8 Therefore, several advances in filling solutions have occurred that provide more appropriate filling solutions for the micro-environment that exists between the lens and the cornea. One such solution is a sterile 0.9% sodium chloride that is available in 5mL preservative-free vials. Another is a sterile 10mL preservative-free solution that contains boric acid, sodium borate, and sodium chloride. And, a third solution is available in sterile 10mL preservative-free vials that contain calcium, potassium, magnesium, sodium, and phosphate; this solution attempts to mirror the essential electrolytes in the human tear film.

OTHER SCLERAL LENS UTILIZATION

Corneal ectasias, specifically keratoconus, have received much of the attention of scleral lens applications because of the advantages that sclerals provide. They may provide such patients with the opportunity for a more comfortable, stable wearing experience because these lenses do not rest on the cornea. Additionally, some patients may experience improved vision, because the optical zone in scleral lenses is often larger than in small-diameter GP lenses. Additionally, small-diameter GP lenses will typically follow the steepest portion of the cornea, which can create additional optical challenges if the steepest regions of the cornea are decentered.

Although keratoconus patients may benefit from scleral lenses, there are several other corneal conditions that could be helped with scleral lenses. Here we will review those conditions and the specific considerations for each of them.

Corneal Compromise By design, scleral lenses not only provide the ocular surface with a new refracting surface, they also provide a moisture chamber between the posterior surface of the lens and the anterior surface of the cornea. As such, although scleral lenses are often thought of in situations in which vision would be the primary reason for fitting the lenses, certain patients can benefit from the moisture chamber provided by scleral lenses. Consider scleral lenses in patients who have any condition that could cause corneal compromise to the ocular surface including severe dry eye, exposure keratopathy, graft-versus-host disease, post-refractive surgery dryness, and any other non-infectious disease requiring chronic management of a compromised cornea.^9-11

Scleral lenses will often be supplementary to other treatment efforts. Consider this example: Patients who have Sjögren’s keratoconjunctivitis sicca are often taking prescription medications and may even be undergoing advanced procedures to rehabilitate the ocular surface. However, often with these patients, corneal rehabilitation is difficult without the addition of more advanced strategies such as scleral lenses. Be sure to appropriately educate patients on when and how they should be using their medications so that they utilize them safely in coordination with their scleral lenses.

Patients who have corneal compromise tend to be more straightforward from a fitting perspective because their corneas are not ectatic. This removes a variable that sometimes makes the more advanced keratoconus patients more difficult to fit. Be cognizant of the landing zone characteristics, as this is always critical for successful scleral lens fits. Anecdotally, these patients seem more prone to fogging of the post-lens tear film. Any level of scleral landing zone misalignment may exacerbate this because of the altered health of the tear film¹² (Figure 1).

In conditions in which the cornea is severely compromised, optimizing the surface characteristics of the lens is critical, because insufficient tear quality will challenge lens wearers. Fortunately, because of the moisture chamber created and the lid being blocked from contacting the compromised cornea, these patients will often feel much better with the scleral lens on the eye. Additionally, there is evidence that buffered filling solutions in the bowl of the lens may provide additional comfort for these patients.⁷ PEG treatment should be utilized in these situations to optimize the lid-lens interaction, promoting a more optimized environment.

One of the benefits in this patient population is the improved best-corrected visual acuity (BCVA) that they often experience. With a compromised cornea, the unfortunate reality is that the BCVA can often be severely reduced because of the poor quality of the cornea and tear film, which are the primary external refracting surfaces. Scleral lenses re-normalize the visual quality in these patients, often dramatically improving BCVA (Figure 2).

Epithelial Basement Membrane Dystrophy (EBMD) Because it represents the most common corneal dystrophy,^13,14 it is critical to understand the underlying pathophysiology of EBMD and how to optimally identify these patients as well as how scleral lenses provide an opportunity for improved visual outcomes.

EBMD is a condition in which aberrant basement membrane is produced by the basal corneal epithelial cells, causing irregular ridges of the basement membrane to protrude anteriorly into the corneal epithelium.¹⁵ As such, it can create irregular ridges in the epithelium leading to map, dot, and fingerprint patterns in the cornea. In more severe cases, this can be visualized at the slit lamp using a standard white light assessment. It is much more easily assessed after fluorescein has been placed on the ocular surface and viewed with a cobalt blue light and Wratten #12 filter. Negative staining will accentuate the ridges created by aberrant basement membrane.

Patients who have EBMD are at an increased risk of developing recurrent corneal erosions (RCEs). Early on in the condition, these patients may present with complaints such as mild ocular discomfort and vision that is variable secondary to the integrity of the tear film; there may also be elevations that can vary in location on the cornea over time. Additionally, these patients may have needed multiple glasses remakes until the underlying cause of the variability was identified. They will often manifest changes in the amount of astigmatism and also the axis at which the astigmatism is located.

Treatment includes education and artificial tears for mild conditions. In more severe cases in which RCEs are occurring or vision is significantly affected, more aggressive treatments can be pursued. These include phototherapeutic keratectomy (PTK) or manually debriding the cornea in an attempt for the cornea to re-epithelialize with a more normal basement membrane; ideally, this will minimize epithelial irregularities and will reduce the chance of further RCEs.¹⁶

Scleral lenses can play a tremendous role for these patients via re-normalizing the ocular surface. Some patients will prefer to not undergo any surgical procedures if possible. Additionally, even with manual debridement or PTK, there may still be irregularities that recur in these patients, resulting in an irregular refracting surface. A scleral lens provides a regular surface and can dramatically improve these patients’ BCVA (Figure 3).

The scleral lens fitting process for these patients is fairly straightforward. Although these patients have irregular areas of elevation, their corneas usually have a relatively normal shape. Keep in mind that these patients will have a notable difference in their BCVA between the scleral lenses and their glasses. Interestingly, even though these patients can often manifest significant levels of refractive astigmatism, the scleral lens prescription will infrequently require astigmatic correction because of the irregularities in the cornea.

Corneal Scarring Several conditions can cause permanent corneal scarring. This can include a corneal injury, any infectious event causing long-term scarring, severe inflammatory conditions, or altered corneas secondary to surgical modification.^17,18 Often, these corneas have severe irregularities that add to the complexities of providing adequate best-corrected vision for these patients. Although irregularities in the stroma are easily visible at the slit lamp and topography maps will exhibit irregular patterns, experience has demonstrated that irregularities in epithelial thickness are present as well (Figure 4).

As long as there is not severe scarring through the visual axis, these patients will often experience significant improvements in visual acuity when fit with a scleral lens. Additionally, as long as there is not severe deformity in the cornea, the shapes of these corneas are often relatively regular. There may be localized areas of irregularities, but if the total corneal shape is similar to a normal cornea, these fits can be relatively straightforward.

Post-Refractive Surgery Corneas We are fortunate that the majority of our refractive surgery patients are without complications. But, there are situations in which irregularities compromise a patient’s visual quality. Refractive corneal procedures have advanced significantly, but they are not without visual risks. Radial keratotomy (RK) is more challenging because of the fact that the RK scars can interfere with the pupil—and cause visual compromise—when it is dilated in low light levels.¹⁹ Additionally, these incisions could potentially create irregularities in the cornea.^19,20

As refractive procedures advanced, photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) have improved outcomes for our patients. In these procedures, the cornea assumes a new, more oblate shape created by the central flattening of the cornea. As such, the cornea now has a new dynamic.

For post-refractive surgery patients who require refractive correction but may not qualify for an enhancement procedure, soft contact lenses are an option. But, challenges arise with the new oblate profile of these corneas. As such, when a traditional soft lens is placed on the eye, often there is a vaulting over the cornea that results in a temporary fluctuation of vision. As patients blink, the lens is forced to the cornea, causing a temporary clearing of vision followed by a blurring that results as their eyes stay open.

This single fact makes it difficult for these patients to wear traditional soft lenses. These patients do have other options. Certainly, one of those options is a small-diameter GP contact lens designed with reverse curves to conform to the new corneal anatomy. Additionally, because it is rigid, the lens can compensate for any irregularities in the cornea that require correction.^21-23

Scleral lenses are also an option for these patients.²⁴ We need to be cognizant of the oblate shape of these corneas, as the scleral lenses utilized for these patients often require significantly less sagittal depth compared to scleral lenses for those who have keratoconus. Fortunately, many contemporary scleral lens designs have incorporated a reverse curve in the region of limbal clearance that inherently makes the lens design optimized for these corneas²⁵ (Figure 5). When fitting scleral lenses on these eyes, be aware of the central corneal clearance, and make sure that it appropriately meets the accepted guidelines of clearance between 50µm to 200µm after lens settling.²⁶

Post-refractive surgery ectasia can also create fitting obstacles but can be successfully fit with scleral lenses to improve patients’ visual outcomes.²⁷ In instances in which corneal ectasia is present, similar fitting strategies are used with these corneas as are used with keratoconic corneas.

Corneal Transplant Corneal transplants have restored vision for individuals who had severe corneal conditions requiring a new refractive surface. With new corneal tissue present, there is enhanced awareness of preserving corneal health. As such, and with the thought of optimizing oxygen transmission to the transplanted tissue, most eyecare practitioners will initially fit these corneas with small-diameter GP lenses that help optimize oxygen transmission.

When small-diameter lenses do not provide an appropriate fit, are uncomfortable for a patient, or provide inadequate vision, scleral lenses are a viable option. But, special precautions need to be taken to preserve the integrity of the donor tissue. First and foremost, oxygen permeability is of critical importance. This means that clinically, there are two major factors that practitioners need to consider: 1) the oxygen transmissibility of the material that is utilized; and 2) the amount of clearance of the lens over the cornea. Reach for the highest-oxygen-permeable materials to which you have access. Additionally, while there is a range of clearance above the cornea that is deemed acceptable for most patients, for those patients who have received a corneal transplant, minimum acceptable corneal clearance is usually the goal; this often means being as close as possible to 50µm of clearance after settling of the lens.

Additionally, although we always aim for adequate limbal clearance with any of our scleral lens fits, be additionally cautious in the limbal region of these patients, because the host limbal region is often what provides the renewed epithelium for the donor tissue. I tend to reach for a slightly larger lens in these individuals to ensure adequate clearance without requiring too much of a reverse curve between the landing zone and the limbal clearance zone—this can bear unfavorably at the proximal portion of the landing zone. Additionally, closely observe the superior corneal limbal region, in particular the superior nasal region. Although each patient’s scleral shape influences the way that the lens rests on the sclera, simple gravity tends to want to move the lens inferiorly. And because the nasal sclera tends to be flatter compared to the temporal sclera, if lenses do decenter, they tend to do so inferior-temporally.

High Regular Astigmatism Although practitioners typically think of scleral lenses for irregular corneas, they sometimes forget to consider scleral lenses as options for their non-irregular cornea patients. A population that I have seen benefit tremendously from this are those individuals who have high amounts of regular astigmatism. I have fit patients who had previously tried soft toric, GP, and hybrid lens designs but did not acquire the visual outcome for which they were looking or had difficulties adapting to the lenses; I have transitioned patients from these lenses to scleral lenses as well.

When a patient’s refractive astigmatism is corneal, wearing a rigid lens can create a tear lens that could optically correct the astigmatism. As a scleral lens is filled with nonpreserved solution, it inherently creates a fluid shell, forming a tear lens in a very similar way.

There are a few factors for which you should be prepared if you are fitting patients who have high amounts of regular astigmatism. It is difficult to predict the shape of most patients’ scleras without measuring the topography with advanced technologies or simply placing a lens on the sclera and assessing its shape; however, there is a high level of certainty that if patients have high levels of regular corneal astigmatism, then it will likely extend to the sclera as well.²⁸ Expect a need for toric peripheral curves in these patients. Often these patients will require more toricity in the landing zone than what is typically present with standard toric peripheral curves in most scleral lens fitting sets.

This is advantageous in the fitting of scleral lenses for these patients because the toricity will often be sufficient to lock the lens in place at a certain axis. This gives the advantage of being able to add additional astigmatic power to the lens in a reliable way if it needs to be placed in the lens. Keep in mind that with higher levels of corneal astigmatism, this toricity does tend to extend on the sclera more predictably than irregular corneal toricity does.²⁸

The further away from the limbus that we travel on the sclera, the more irregular the sclera becomes.³ For high regular corneal astigmatic patients whom I fit with scleral lenses, I attempt to work with slightly smaller-diameter lenses so that the landing zone can be closer to the limbal region while always respecting appropriate limbal clearance.

CONCLUSION

The adoption of scleral lenses for vision correction of keratoconus patients has revolutionized the way that practitioners can provide care. Additionally, there are several other patients who may also benefit from scleral lenses. Consider these alternative uses for scleral lenses. CLS

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